Coulometric Anodic Stripping Voltammetry of Lead at Copper Column Electrode

A flow coulometric electroanalytical system using a copper column electrode with a copper wire inserted into a Nafion tube was developed to determine Pb(II) content based on anodic stripping voltammetry. The electrolysis efficiency of 5 μM Pb(II) was evaluated to be 100.4±4.5 % (n=5) when the length of the copper wire and flow rate of the Pb(II) solution were 50 cm and 0.1 mL min⁻¹, respectively. The amount of electricity due to the re-oxidation of Pb electrodeposited at the copper column electrode was proportional to the concentration of Pb(II) in the range between 0.1 to 100 μM, and the limit of detection for Pb(II) was 0.8 μM for a deposition time of 15 min. Interference from the presence of Cd(II) could be avoided and the selective determination of Pb(II) was successfully achieved by adjustment of the electrodeposition potential.     

Fully automated immunoassay for detection of prostate-specific antigen using nano-magnetic beads and micro-polystyrene bead composites, 'Beads on Beads'

Magnetic beads have served as a conventional bioassay platform in biotechnology. In this study, a fully automated immunoassay was performed using novel nano- and microbead-composites constructed by assembling nano-magnetic beads onto polystyrene microbeads, designated ‘Beads on Beads’. Nano-sized bacterial magnetic particles (BacMPs) displaying the immunoglobulin G (IgG)-binding domain of protein A (ZZ domain) were used for the construction of ‘Beads on Beads’ via the interaction of biotin-streptavidin. The efficient assembly of ‘Beads on Beads’ was performed by gradual addition of biotin-labeled BacMPs onto streptavidin-coated polystyrene microbeads. Approximately 2000 BacMPs were uniformly assembled on a single microbead without aggregation. The constructed ‘Beads on Beads’ were magnetized and separated from the suspension by using an automated magnetic separation system with a higher efficiency than BacMPs alone. Furthermore, fully automated detection of prostate-specific antigens was performed with the detection limit of 1.48 ng mL⁻¹. From this preliminary assay, it can be seen that ‘Beads on Beads’ could be a powerful tool in the development of high-throughput, fully automated multiplexed bioassays.     

Characterization of creaming precipitate of tea catechins and caffeine in aqueous solution

The content of a crude precipitate formed by creaming, which was made from a catechin mixture and caffeine, was investigated by an integral volume of H-2 proton signals of tea catechins in the (1)H-NMR spectrum. Gallated catechins formed a crude precipitate more predominantly than non-gallated catechins. The 2,3-cis-non-gallated catechin (-)-epicatechin (EC) formed a 1?:?1 complex with caffeine, and 2,3-cis-gallated catechin (-)-epicatechin gallate (ECg) formed a 2?:?4 complex with caffeine. The π-π complexation site of EC with caffeine was only the A ring, whereas that of ECg included all aromatic rings, A, B, and B'. It was thought that the hydrophobicity of the 2?:?4 complex of ECg and caffeine was stronger than that of the 1?:?1 complex of EC and caffeine, with the result that the 2?:?4 complex of ECg and caffeine precipitated by creaming more predominantly than the 1?:?1 complex of EC and caffeine in aqueous solution.     

Simultaneous assay of the activities of two key enzymes in cholesterol metabolism by gas chromatography-mass spectrometry

A very sensitive and specific method for the simultaneous assay of the activities of two key regulatory enzymes in cholesterol metabolism, 3-hydroxy-3-methylglutaryl-coenzyme A (HMG-CoA) reductase (EC 1.1.1.34), and cholesterol 7 alpha-hydroxylase (EC 1.14.13.7), is described. The assay is based on the measurement of [2H3]mevalonolactone and 7 alpha-hydroxycholesterol produced by the incubation of [2H3]HMG-CoA and endogenous cholesterol with hamster liver microsomes using isotope dilution mass spectrometry. The incubation mixture was purified by means of solid extraction cartridges, and the extract was treated with benzylamine followed by dimethylethylsilyl imidazole. The resulting ether derivatives of the mevalonylbenzylamide and 7 alpha-hydroxycholesterol were quantified by gas chromatography-mass spectrometry with selected-ion monitoring in a high resolution mode. The method made it possible to assay simultaneously the activities of HMG-CoA reductase and cholesterol 7 alpha-hydroxylase in hamster liver microsomes with high sensitivity and accuracy.     

Proton magnetic resonance imaging of flow motion of heavy water injected into a hollow fiber dialyzer filled with saline

Observations using MRI were performed for the motion of heavy water injected into a hollow fiber dialyzer. A cylindrical dialyzer houses a bundle of 10,000 hollow fibers. Because blood components permeate through the hollow fiber membrane from the interior to the exterior of the hollow fiber, which is the dialysate flow path, uniformity of dialysate flow is required. The dialyzer was initially filled with saline and heavy water was injected into the inlet port of the dialysate flow path. MRI tuned for protons could distinguish the injected heavy water from the already present saline. Due to the specific gravity difference, MRI could observe the sedimentation of the injected heavy water flowing beneath the already present saline. The uniformity of the dialysate flow was supported by the finding that the injected heavy water brought about uniform sedimentation and distributed the already present saline uniformly throughout the entire volume of the dialyzer.     

Nine regioisomeric and stereoisomeric triterpene dimers from Maytenus chuchuhuasca

Nine regioisomeric and stereoisomeric triterpene dimers, namely xuxuarine Falpha (1), isoxuxuarine Falpha (2; cangorosin B), 7,8-dihydroisoxuxuarine Falpha (3), isoxuxuarine Gbeta (4), 7,8-dihydroisoxuxuarine Galpha (5), isoxuxuarine Ebeta (6), 7alpha-hydroxyisoxuxuarine Ealpha (7), 7',8'-dihydroxuxuarine Aalpha (8), and 7',8'-dihydroxuxuarine Dbeta (9), were isolated from the Brazilian medicinal plant "xuxuá" (Maytenus chuchuhuasca). Their structures have been elucidated based on several spectroscopic analyses including 2D-NMR experiments, MS spectra and CD spectral studies.     

Synthesis of [L-Ala-1]RA-VII, [D-Ala-2]RA-VII,and [D-Ala-4]RA-VII by epimerization of RA-VII,an antitumor bicyclic hexapeptide from Rubia plants,through oxazoles

Three epimers of a natural cyclic hexapeptide RA-VII were prepared via formation of oxazoles from thioamides or thioimidates of RA-VII followed by hydrolysis. They are the epimers at l-Ala-1, d-Ala-2, and d-Ala-4, respectively. The one having l-Ala-1 adopted trans-cis-trans-trans-trans-trans (t-c-t-t-t-t) amide configurations in the crystal, a type-VI beta-turn for residues 1-4 stabilized by one intramolecular hydrogen bond between Ala-4 NH and l-Ala-1 C = O, and in CDCl(3) existed as a mixture of six conformers, of which the major conformer was very similar to that in the crystal, but quite different from that of RA-VII in solution. The second epimer, having d-Ala-2 had in the crystalline state t-t-t-t-c-t amide configurations, a gamma-turn at Tyr-3 stabilized by two intramolecular hydrogen bonds between d-Ala-2 NH and Ala-4 C = O and between Ala-4 NH and d-Ala-2 C = O, and existed in CDCl(3) as a single conformer, the structure of which was very similar to its crystal structure, and to the crystal structure of peptide 25 except for the backbone and the side chains at residues 1 and 2. The third epimer, having d-Ala-4 had t-c-t-t-c-t amide configurations in the crystal, a type-VI beta-turn for residues 1-4 as observed in the first epimer, and in CDCl(3) existed in three conformers, of which the major one was similar to that in the crystal but different from that of RA-VII in solution. The three epimers showed very weak cytotoxicity on P-388 leukemia cells, which may be because of their conformational differences from the active conformation of RA-VII.